1. Field of the Invention
This invention relates to a polymer having acid labile groups of at least one type and crosslinked with a crosslinking group having a C--O--C linkage within a molecule and/or between molecules. It also relates to a chemically amplified positive resist composition comprising the polymer as a base resin which has a high alkali dissolution contrast before and after exposure, high sensitivity and high resolution and is thus suitable as a fine pattern forming material for use in the manufacture of ultra-LSIs. It further relates to a method for forming a resist pattern using the composition.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. Under such circumstances, deep-ultraviolet lithography is regarded promising as the next generation of fine patterning technology. The deep-UV lithography is capable of working on the order of 0.5 .mu.m or less and makes it possible to form a resist pattern having a side wall nearly perpendicular to the substrate if a less light absorbing resist material is used.
A number of chemically amplified positive working resist materials using acid catalysts were recently developed as disclosed in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. Nos. 4,491,628 and 5,310,619. They utilize a high illuminance KrF excimer laser as a deep-UV source. Since these materials have high sensitivity, resolution and dry etching resistance, they are promising as resist materials especially suited for deep-UV lithography.
The chemically amplified, positive resist materials being known include those of the two-component system comprising a base resin and a photoacid generator and those of the three-component system comprising a base resin, a photoacid generator, and a dissolution inhibitor having an acid labile group.
JP-A 115440/1987 discloses a resist composition comprising poly-4-tert-butoxystyrene and a photoacid generator. Similarly, JP-A 223858/1991 discloses a two-component system resist composition comprising a resin having a tert-butoxy group in its molecule and a photoacid generator and JP-A 211258/1992 discloses a two-component system resist composition comprising a polyhydroxystyrene containing a methyl, isopropyl, tert-butyl, tetrahydropyranyl or trimethylsilyl group in its molecule and a photoacid generator.
Furthermore, JP-A 100488/1994 proposes a resist composition comprising a polydihydroxystyrene derivative such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene], and poly[3,5-bis(2-tetrahydropyranyloxy)styrene] and a photoacid generator.
The base resins used in these resist compositions have an acid labile group in a side chain. If the acid labile group is a strong acid-decomposable one such as a tert-butyl and tert-butoxycarbonyl group, the acid labile group is deactivated through reaction with air-borne basic compounds and becomes unlikely to decompose. Such a resist composition tends to form a pattern having a T-top profile. On the other hand, if the acid labile group is an alkoxyalkyl group such as ethoxyethyl which is decomposable with weak acid, the resist composition is little affected by air-borne basic compounds, but forms a pattern which will become extremely thin with the lapse of time from exposure to heat treatment. The inclusion of a bulky group in a side chain can detract from heat resistance. The composition is less satisfactory in sensitivity and resolution. None of the resist compositions thus far proposed are practically satisfactory. There is a desire to overcome these problems.